The present invention relates to connection switching at a node constituting a network and, more particularly, to a connection switching method and apparatus upon occurrence of a fault.
In a ring network constituted by connecting a plurality of nodes in a loop, a signal identical to a normal transmission signal is generally transmitted as a spare signal in the same direction. When a fault occurs on a normal line between certain nodes, the connection between these nodes is switched to a spare line to avoid signal disconnection. This connection switching is performed by a switch, e.g., a cross-connection apparatus arranged at the node.
Conventional cross-connection switching control is described in a firmware program. Every time connection must be switched upon occurrence of a fault, the program must be activated to calculate a connection switching destination. Particularly when a plurality of faults occur, the program is executed for each fault, a long time is required to complete the connection, and connection cannot be switched at a high speed. In some cases, connection is transiently switched.
Further, programs equal in number to the types of faults are necessary. If multiple faults occur, the program repetitively branches and recurs, and the control flow cannot be theoretically grasped. Accordingly, bugs may be included in the firmware program.
It is an object of the present invention to provide a switching method and apparatus capable of completing connection switching within a short time.
It is another object of the present invention to provide a switching method and apparatus capable of achieving high-speed connection switching even upon occurrence of multiple faults.
It is still another object of the present invention to provide a switching method and apparatus capable of easily grasping the switching control flow even upon occurrence of multiple faults.
In order to achieve the above objects, according to the present invention, there is provided a connection switching method of a switch for selectively setting a connection path between a plurality of input lines and a plurality of output lines, comprising the steps of defining the types of faults which may occur on the input lines, storing connection destination information indicating connection states of the switch in accordance with the types of faults, specifying the type of fault on the basis of the defined types of faults when a fault occurs on an input line, reading out connection destination information corresponding to the specified type of fault, and switching the connection state of the switch on the basis of the readout connection destination information.